Adaptive noise cancellation

Abstract

In some embodiments a noise cancellation system includes a first digital microphone to detect ambient noise, a first sigma delta modulator coupled to an output of the first digital microphone, a second digital microphone located near an earpiece speaker to detect an output of the earpiece speaker, a second sigma delta modulator coupled to an output of the second digital microphone, a decimator coupled to the second sigma delta modulator, and an adaptive digital filter to adaptively adjust an output of the earpiece speaker in response to the decimator and the first sigma delta modulator so that the output of the earpiece speaker includes a desired audio and an acoustic signal to cancel some or all of the ambient noise. Other embodiments are described and claimed.

1 . A noise cancellation apparatus comprising:
 a first digital microphone to detect ambient noise;   a first sigma delta modulator coupled to an output of the first digital microphone;   a second digital microphone located near an earpiece speaker to detect an output of the earpiece speaker;   a second sigma delta modulator coupled to an output of the second digital microphone;   a decimator coupled to the second sigma delta modulator;   an adaptive digital filter to adaptively adjust an output of the earpiece speaker in response to the decimator and the first sigma delta modulator so that the output of the earpiece speaker includes a desired audio and an acoustic signal to cancel some or all of the ambient noise.   
     
     
         2 . The noise cancellation apparatus of  claim 1 , wherein sampling rates of the ambient noise provided to the adaptive digital filter and of an output of the decimator are twice that of a base rate. 
     
     
         3 . The noise cancellation apparatus of  claim 1 , wherein sampling rates of the ambient noise provided to the adaptive digital filter and of an output of the decimator are not the same. 
     
     
         4 . The noise cancellation apparatus of  claim 1 , wherein the sampling rate of the ambient noise provided to the adaptive digital filter is two times a base rate and the sampling rate of the output of the decimator is four times the base rate. 
     
     
         5 . The noise cancellation apparatus of  claim 1 , wherein an order of the decimator is lower than an order of the first sigma delta modulator and/or of the second sigma delta modulator. 
     
     
         6 . The noise cancellation apparatus of  claim 5 , wherein the decimator is a first, second, or third order decimator and wherein the first sigma delta modulator and the second sigma delta modulator are fourth order sigma delta modulators. 
     
     
         7 . The noise cancellation apparatus of  claim 1 , wherein the first sigma delta modulator is a sigma delta analog-to-digital modulator and the second sigma delta modulator is a sigma delta analog-to-digital modulator. 
     
     
         8 . The noise cancellation apparatus of  claim 1 , further comprising one or more decimators coupled between the first sigma delta modulator and the adaptive digital filter. 
     
     
         9 . The noise cancellation apparatus of  claim 1 , further comprising an adder to combine an output of the adaptive digital filter and the desired audio. 
     
     
         10 . The noise cancellation apparatus of  claim 1 , wherein the adaptive digital filter is to mitigate delays of the decimator. 
     
     
         11 . The noise cancellation apparatus of  claim 1 , further comprising a sigma delta modulator coupled between an output of the adaptive digital filter and an input of the earpiece speaker. 
     
     
         12 . The noise cancellation apparatus of  claim 1 , further comprising a first delay coupled between the first sigma delta modulator and the adaptive digital filter, a second delay coupled between the adaptive digital filter and the earpiece speaker, a third delay coupled between the second sigma delta modulator and the decimator, and/or a fourth delay coupled between the decimator and the adaptive digital filter. 
     
     
         13 . The noise cancellation apparatus of  claim 1 , wherein the decimator includes a sinc filter. 
     
     
         14 . The noise cancellation apparatus of  claim 1 , wherein sampling rates of the ambient noise provided to the adaptive digital filter and of an output of the decimator are higher than that of a base rate and wherein an order of the decimator is lower than an order of the first sigma delta modulator and/or of the second sigma delta modulator. 
     
     
         15 . A method of noise cancellation comprising:
 detecting an ambient noise with a first digital microphone;   sigma delta modulating an output of the first digital microphone;   detecting an output of an earpiece speaker with a second digital microphone;   sigma delta modulating an output of the second digital microphone;   decimating the sigma delta modulated output of the second digital microphone;   adaptively adjusting an output of the earpiece speaker in response to the decimating and the sigma delta modulating of the output of the first digital microphone so that the output of the earpiece speaker includes a desired audio and an acoustic signal to cancel some or all of the ambient noise.   
     
     
         16 . The method of  claim 15 , further comprising sampling the ambient noise at a sampling rate that is twice that of a base rate and decimating the sigma delta modulated output of the second digital microphone at the sampling rate that is twice that of the base rate. 
     
     
         17 . The method of  claim 15 , further comprising sampling the ambient noise at a first rate and performing the decimating at a second rate that is different than the first rate. 
     
     
         18 . The method of  claim 15 , further comprising sampling the ambient noise at a sampling rate that is twice that of a base rate and decimating the sigma delta modulated output of the second digital microphone at the sampling rate that is four times that of the base rate. 
     
     
         19 . The method of  claim 15 , wherein an order of the decimating is lower than an order of the sigma delta modulating of the output of the first digital microphone and/or an order of the sigma delta modulating of the output of the second digital microphone. 
     
     
         20 . The method of  claim 15 , further comprising combining the desired audio signal. 
     
     
         21 . The method of  claim 15 , further comprising mitigating delays in the decimating. 
     
     
         22 . The method of  claim 15 , further comprising sampling the ambient noise at a sampling rate that is higher than that of a base rate and decimating the sigma delta modulated output of the second digital microphone at a sampling rate that is higher than that of the base rate, wherein an order of the decimating is lower than an order of the sigma delta modulating of the output of the first digital microphone and/or an order of the sigma delta modulating of the output of the second digital microphone.